1. Field of the Invention
The present invention relates to transmitter, and more particularly, to transmitter which is able to transmit an electric signal precisely representing a pressure on the transmitter.
2. Description of the Prior Art
Touch panel or touch sensitive screen is important human machine interface in modern age. In addition to detecting approximation or touch of human body, touch panel is also used for detecting approximation or touch of stylus or tip of stylus such that user is able to precisely control a trace painted by a touching tip.
Stylus may actively emit electric signal via its tip. In this present application, it is called active stylus. When the tip approximating or touching a touch panel, electromagnetic response of the electric signal occurs to electrodes of the touch panel. By detecting the electromagnetic response corresponding to the electric signal, the stylus approximating or touching the sensing electrodes could be detected. Therefore a position of the tip relative to the touch panel could be concluded accordingly.
Traditional active stylus includes wired and wireless types. Wired active stylus is electrically supplied via a connection cable to the touch panel. Besides, signals such as one representing tip pressure could be transmitted to the touch panel via the connection cable. The most noticeable shortcoming of wired active stylus is inconvenience of the connection cable. However, wireless active stylus has to solve synchronization problem between the active stylus and the controller detecting the active stylus. Wired active stylus does not have such problem.
Moreover, a difference between active and passive stylus is that active stylus may sense pressure on itself. Since pressure sensor of active stylus could sense pressure level the tip is pressed, the controller detecting the active stylus or the host may gather the information. However, how to transmit the pressure level to the controller is another problem required to be solve in this field. For example, in case the information is transmitted wirelessly, cost and power consumption would be increased accordingly. Besides, the controller and the host needs to have wireless communication capability. Thus the system gets complicated accordingly. In another instance, the pressure level of the tip could be modulated and represented by amplitude of analogue signal. It may be easily misjudged or erroneous demodulated by environmental changes of temperature or moisture, various distance between the tip and the touch panel, and noise interference.
Hence, it is required to have active stylus transmitting electric signal which precisely reflects the pressure level.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.